Chip resistors are resistors in which a resistance film is coated on a substrate and which is surface mounted on a printed circuit board. To permit for ease of mounting a chip resistor on a printed circuit board, the resistor has no leads or terminals projecting therefrom, but merely has metal termination films at each end of the resistance film which terminal films extends onto a surface of the substrate opposite that on which the resistance film is located. The terminal films are then mounted on the surface of the printed circuit board and soldered to conductive strips on the board.
Resistors generate heat which must be dissipated from the resistor to prevent overheating of the resistor and the possibility of burning out the resistor. High power resistors generate considerable heat which must be conducted away from the resistor by either conduction to the printed circuit board through the terminal films, by convection or by radiation. One technique which has been developed to provide greater conduction of heat from the resistor to the printed circuit board is to increase the size of the termination films on the surface of the substrate opposite the resistance film. The larger termination films conduct a larger amount of heat from the resistor. One such resistor is shown in U.S. Pat. No. 5,739,743 to J. B. Mazzochette, issued Apr. 14, 1998, entitled ASYMMETRIC RESISTOR TERMINAL. Another technique which has been developed is to provide a metal film heat sink on the surface of the substrate opposite the resistance film to conduct additional heat from the resistor. Such a resistor is shown in U.S. Pat. No. 5,179,366 to R. Wagner, issued Jan. 12, 1993, entitled END TERMINATED HIGH POWER CHIP RESISTOR ASSEMBLY. However, a problem with each of these types of resistors is that there is a metal film, either a portion of the termination film or a heat sink film, which is directly opposite the resistance film. This provides a capacitance between the resistance film and the opposing metal film. Such a capacitance is undesirable in a high power resistor which operates at RF. Therefore, it would be desirable to have a high power resistor which has good heat dissipation but minimizes any capacitance between the resistance film and a metal film on the substrate.